EP0481610B1 - Verfahren und Gerät zur Entfernungsvektorlenkung in Punkt-zu-Punkt Datagram Verbindungen - Google Patents

Verfahren und Gerät zur Entfernungsvektorlenkung in Punkt-zu-Punkt Datagram Verbindungen Download PDF

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Publication number
EP0481610B1
EP0481610B1 EP91308670A EP91308670A EP0481610B1 EP 0481610 B1 EP0481610 B1 EP 0481610B1 EP 91308670 A EP91308670 A EP 91308670A EP 91308670 A EP91308670 A EP 91308670A EP 0481610 B1 EP0481610 B1 EP 0481610B1
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Prior art keywords
distance vector
sequence number
packet
router
update
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French (fr)
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EP0481610A3 (en
EP0481610A2 (de
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Radia Joy Perlman
George Arthur Harvey
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Cabletron Systems Inc
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Cabletron Systems Inc
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L45/00—Routing or path finding of packets in data switching networks
    • H04L45/02—Topology update or discovery
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L45/00—Routing or path finding of packets in data switching networks
    • H04L45/44—Distributed routing
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L45/00—Routing or path finding of packets in data switching networks
    • H04L45/02—Topology update or discovery
    • H04L45/033—Topology update or discovery by updating distance vector protocols

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  • This invention relates generally to a protocol used in interconnected computer networks known as distance vector routing and, more specifically, to distance vector routing for use in interconnected networks having point-to-point links for transmission of messages in a "datagram" environment.
  • nodes Application-to-application data transfer between two interconnected computers or "nodes" in a network is accomplished by logically building functions in a series of layers, where each layer uses the services of the layer immediately below, adds functions of its own, and presents a richer service to the layer immediately above.
  • Each layer in a node that is the source of a message or information packet logically communicates with its peer layer in a destination node, but does so by using the services of the layer immediately below.
  • the present invention concerns only the bottom three layers, commonly known as:
  • LANs Local Area Networks
  • PPP datagram point-to-point protocol
  • each router node X is responsible for informing each of X's neighbors about X's distance to each destination in the network. X calculates its own distance to each destination based on its neighbor's reported distances to that destination. Thus X's distance to a particular destination must be reliably delivered to each neighbor, unless X's recomputation of its distances results in a different distance to that destination before the previous value is successfully transmitted. In this case the previous value need not be transmitted, and instead the new value must be transmitted.
  • a significant problem with a conventional distance vector routing protocol is that, if the data link layer provides datagram service to the network layer, the protocol has no way of ensuring that updated distance vectors will reach their destinations.
  • One solution that has been proposed is to have each router retransmit its distance vector to neighboring routers on a periodic basis, whether or not any changes have occurred in the distance vector. The theory underlying this approach is that if any updated distance vector does not reach its destination, the likelihood is that the next periodic transmission will be made without error.
  • This approach is used in a datagram data link layer protocol known a PPP (for point-to-point protocol). Its principal disadvantage is that it incurs unnecessary overhead. Distance vectors are updated whether or not they have changed, which results in significant unnecessary message traffic between routers.
  • the approach has also been applied to local area networks, as distinguished from point-to-point links, since it was once perceived that the bandwidth of LANs was abundant.
  • EP-A-0348331 discloses a method of updating topology databases of nodes in a network by broadcasting update messages. Each node which "owns" a resource added or deleted from the network broadcasts a topology database update message to each of its neighbouring nodes.
  • the present invention resides in a method, and corresponding apparatus, for providing current distance vectors for use in multiple routers in an interconnected computer system. Updates to the distance vectors are transmitted only when a change has occurred in the distance vector data, and the routers may be connected by point-to-point links that provide datagram service.
  • the method of the invention comprises the steps of detecting changes in a distance vector stored in a router; then, upon the detection of a distance change for a destination in the distance vector, setting a Send Flag corresponding to that destination and corresponding to every neighboring router; detecting the availability of a link to a selected neighboring router n; and transmitting an information packet to the neighboring router n over the available link, the information packet containing as many as possible of the distance vector update items that are flagged by Send Flags associated with router n.
  • the method also includes the steps of selecting a unique sequence number for transmission with the packet; storing the sequence number in a sequence number field SN(d,n) for each update item transmitted with the packet; receiving an acknowledgment message from the neighboring router n, containing the same unique sequence number that was transmitted with the information packet; and clearing the sequence number field in every location of the distance vector in which the unique sequence number is stored, to indicate successful transmission of the corresponding distance vector update item.
  • the method further includes the steps of scanning for the availability of links to other neighboring routers; and repeating, for each available link, the steps of transmitting an information packet, selecting a unique sequence number, storing the sequence number in the distance vector, receiving an acknowledgment message, and clearing the appropriate sequence number fields in the distance vector.
  • distance vector updates are transmitted to all of the neighboring routers as the links to those routers become available.
  • the step of transmitting the information packet includes scanning the distance vector for update items that have not yet been transmitted, storing each located update item in the information packet and, when the packet is full, initiating its transmission.
  • the step of transmitting the information packet may also include the additional steps of checking to determine whether a selected number of destination items in the distance vector have been scanned and, if so, initiating transmission of the packet even if it is not full.
  • the step of scanning the distance vector is performed on a round-robin basis, such that scanning begins, for a particular neighboring router, at a destination item following the one last scanned prior to initiating transmission of the last information packet to the same neighboring router.
  • the method further includes the steps of receiving a distance vector update packet from a neighboring router, updating a distance vector at the receiving router in accordance with the information received in the vector update packet, and transmitting an acknowledgment message to the router from which the update packet was received.
  • the acknowledgment message includes the same unique sequence number that was contained in the received update packet.
  • Another aspect of the invention is that distance vector update items are automatically retransmitted if an acknowledgment is not received within a selected time period.
  • This feature involves the steps of periodically saving the sequence number of the last information packet transmitted by the router; periodically retrieving the sequence number of the last information packet transmitted at a selected time period earlier; and scanning the distance vector for the sequence numbers equal to or less than the retrieved sequence number. These numbers indicate distance vector update items that have been transmitted but not acknowledged during the selected time period. Subsequent steps include clearing any sequence numbers located in the preceding scanning step; and setting the Send Flags corresponding to the sequence numbers that have been cleared in the preceding step. As a result of setting the Send Flags and clearing the sequence numbers of these items, they will be retransmitted.
  • the corresponding apparatus of the invention includes, in general terms, means for detecting changes in a distance vector stored in a router; means responsive to the detection of a distance change for a destination in the distance vector, for setting a Send Flag corresponding to that destination and corresponding to every neighboring router; means for detecting the availability of a link to a selected neighboring router n; and means for transmitting an information packet to the neighboring router n over the available link, the information packet containing as many as possible of the distance vector update items that are flagged by Send Flags associated with router n.
  • the apparatus includes means for selecting a unique sequence number for transmission with the packet; means for storing the sequence number in a sequence number field SN(d,n) for each update item transmitted with the packet; means for receiving an acknowledgment message from the neighboring router n, containing the same unique sequence number that was transmitted with the information packet; and means for clearing the sequence number field in every location of the distance vector in which the unique sequence number is stored, to indicate successful transmission of the corresponding distance vector update item.
  • the present invention represents a significant advance in the field of computer networks.
  • the invention provides a simple but reliable solution to the problems involved in updating distance vectors in routers connected by point-to-point datagram links.
  • the invention avoids the complexities and drawbacks of reliable service, but still ensures that distance vector update items are reliably distributed to neighboring routers.
  • FIG. 1 shows a typical network configuration, including a number of routers or routing destinations, shown as small squares and indicated by reference numeral 10, and a number of non-routing destinations 12, shown as small circles.
  • Local area networks (LANs) 14 are each shown as a line with an arrowhead at each end.
  • Datagram point-to-point links are designated by the letter P. It will be seen that the routers 10 in the illustrative topology are interconnected by datagram point-to-point links. The method to be described operates in this topology over each of the four links 16 that interconnect the routers 10.
  • each router is responsible for maintaining its own distance vector, which is basically a table of the shortest "distances" from the router to each known destination.
  • the vector is generated from a knowledge of the distances to each neighbor destination, and from copies of distance vectors received from each of the neighboring routers.
  • a router On start-up, a router has knowledge only of the distances to the neighboring routers and to non-routing destinations connected to this router.
  • a neighboring router is one that may be reached directly, i.e. without passing through another router or node. Each router initially assumes that the distances to other destinations are infinite.
  • a router On receipt of distance vectors from the neighboring routers, a router computes the shortest distance to each destination, updates its own distance vector accordingly, and transmits the updated vector to its neighboring routers.
  • Each of the routers follows the same procedure, and by an iterative process the distance vectors develop correct and consistent data in all of the routers. This procedure is already well known in the computer network field.
  • the routers perform their intended functions of routing information packets using the shortest or most efficient links for each "hop" of their journey from source to destination.
  • a router becomes aware that its distance vector has changed should it be necessary to transmit a copy of the updated distance vector to the neighboring routers.
  • each update transmitted will be acknowledged by its recipient.
  • the service provided to a router by the data link layer protocol is of the datagram type, under which there is no assurance that an information packet ever reaches its destination.
  • One way of handling the transmission of this update information is to provide a set of Send Flags (SF) for each destination, the set having one flag for each neighboring router.
  • each destination, d, in the distance vector includes a set of Send Flags, SF(d,1) through SF(d,N), where there are N neighboring routers.
  • the Send Flags for that destination are all set to a selected state, such as "1," for all neighboring routers.
  • links to the various neighbors become free, the distance vector update is transmitted and the corresponding Send Flag is cleared.
  • the Send Flags ensure that the update is transmitted to each neighboring router as soon as possible, but do not ensure that the updates are received.
  • one proposal to ensure receipt of distance vector updates in a datagram environment it to transmit the entire distance vector periodically, whether or not changes have occurred. For this approach, all of the Send Flags would be set periodically to initiate the transmissions.
  • a simple mechanism is provided to ensure that distance vector updates that are transmitted only as needed are received by the neighboring routers, even though no reliable service is provided by the data link layer protocol.
  • the invention requires the use of a sequence number associated with each information packet that carries distance vector updates. This sequence number, which uniquely identifies the information packets that carry distance vector updates, is also stored in the distance vector of the originating router.
  • an acknowledgment containing the same sequence number is transmitted back to the originating router, which then modifies its distance vector to indicate that the distance vector updates that were sent in a packet with that sequence number have been successfully received.
  • FIG. 2a shows a distance vector in diagrammatic form, as stored in a router.
  • the distance vector may be thought of as a table having a row for each known destination, the number of which appears in the first column, and having columns in which data relating to the various destinations are stored.
  • One column contains the shortest distance to the destination and another contains the identity of the neighbor through which the destination is reached. Then there are N additional columns, for the total number of neighboring routers.
  • the entries in these columns provide a total of D * N items, where D is the total number of destinations.
  • Each entry (d,n) has two fields: a Send Flag SF(d,n), and a Sequence Number SN(d,n).
  • the Send Flag needs only one bit of data.
  • the length of the sequence number field is a matter of design choice and depends on the potential size of the network configuration. A sequence number field of two bytes (16 bits) is probably adequate for most needs.
  • FIG. 3 shows the principal functions performed in accordance with the method and apparatus of the invention.
  • initialization functions When a router is first placed in operation, there are a number of initialization functions to be performed, as indicated in block 30.
  • the distance vector of FIG. 2a is initialized to reflect that the distances to most destinations are not yet known, and to reflect the known distances to neighbors. Also, various table pointers have to be initialized before starting operation.
  • the method of the invention involves the concurrent performance of a number of different functions, which are briefly described in blocks 34-38, and shown in more detail in FIGS. 4-8. How this concurrency of operations is achieved is not a significant aspect of the invention, and any conventional approach may be used.
  • the several functions described may be performed on a single computer processor, which shares its processing resources among the functions on a time-sliced basis. Alternatively, separate processors operating in parallel may be used to implement the several functions.
  • the five functions will be separately described but it will be understood that they are performed concurrently.
  • pointers d and n used in a function to point to information relating to specific destinations and neighboring routers are maintained separately and independently of similar pointers used in other functions.
  • the destination pointer, d is used in each of four of the functions.
  • the concurrent process mechanism 32 impliedly includes some means of ensuring that the destination and neighbor pointers, d and n, are independently maintained for each of the five concurrently performed functions.
  • each message must be delivered exactly once and in the order sent. Thus, if a first distance vector update were to be sent and lost, a subsequent update for the same neighboring router could not be received and processed without violating the reliable service guarantees.
  • acknowledgment of the receipt of one update is not a prerequisite for receipt and processing of a subsequent update to the same neighboring router, even if the subsequent update relates to the same destination as the first update.
  • the function performed in FIG. 4 is to react to changes in a router's own distance vector.
  • a change occurs when, as a result of data received from neighboring routers, or as a result of network configuration changes that are otherwise conveyed to the router, the router makes a change in its distance vector.
  • the distanced to a destination defined by a pointer d is examined for changes. If there is no change, the value of the pointer d is incremented (block 42), then checked to determine if its maximum value D has been reached (block 44). If so, the pointer is reset to point to destination #1 again (block 46), and processing continues, checking each of the destinations in turn (block 40).
  • the distance vector is modified to request transmission of a distance vector update to each of the neighboring routers.
  • a nonzero sequence number in the distance vector serves as a flag indicating that a distance vector update has been transmitted but not yet acknowledged by a receiving router.
  • a zero sequence number, together with a nonzero Send Flag, indicates to this router that a distance vector update should be transmitted.
  • the function illustrated in FIG. 5 is to scan for availability of communications links to each of the neighboring routers in turn, and to send distance vector updates to the neighboring routers. Performing this function involves two nested loops, one of which checks for link availability for each of the neighboring routers in turn, and the other of which scans through the distance vector to locate updates for transmission.
  • a destination pointer d is set to an initial value obtained from a previously stored location for this particular neighbor n. As indicated in block 60, there are n such stored values, designated dsave(n). Each saved destination pointer indicates a position in the distance vector following the last position from which an update was extracted for transmission to the same neighbor. Keeping these pointers ensures that the distance vector updates are transmitted on a round-robin basis from the distance vector. Because access to the links to neighbors may be limited by the presence of other traffic, some means of scanning the distance vector has to be provided, to ensure that all of the changes that occur eventually get transmitted. If the vector were scanned from the top each time, changes occurring near the bottom of the vector would take longer to be transmitted to the neighbors than changes near the top of the vector Round-robin scanning eliminates this possibility.
  • a new sequence number is obtained (block 62) for use in a packet of data that will next be generated.
  • the new sequence number is stored in an information packet buffer. If no updates are located for transmission to this neighbor n, the same sequence number will be used in the next pass, for neighbor n+1.
  • the sequence number is obtained from a counter (not shown), which will be incremented only upon transmission of the packet. In some instances it may be desirable to use a separate counter for each neighboring router. More generally, the invention requires only that each information packet containing distance vector updates should be uniquely identifiable. A sequence number obtained from a relatively large counter meets this requirement, but other implementations are also possible. For example, the "sequence" number could instead be a random number, so long as there was some provision for eliminating duplicates occurring over a reasonably large time span.
  • a distance vector update is stored in an information packet buffer, as indicated in block 68.
  • the packet can hold multiple distance vector update items, and includes a single sequence number field.
  • the sequence number is also stored in the sequence number field SN(d,n) for this particular destination d and neighboring router n.
  • the corresponding Send Flag SF(d,n) is reset to zero.
  • this item of the distance vector has not been updated or an update was previously sent and is not stored in the packet buffer, i.e. the function of block 68 is bypassed. Then the pointer d is incremented (block 70), and a check is made to determine whether the packet buffer is full (block 72). If the packet buffer is not yet full, the scan for changes in the distance vector will normally continue, in blocks 64 and 66. Incrementing the pointer d in block 70 is, of course, performed in a modulo-D manner, i.e. the pointer is incremented until the maximum value D is reached, then automatically reset to "1" again.
  • processing will continue at block 64, and scanning continues for additional distance vector updates to transmit in the packet being assembled for transmission. If the selected number of destinations has been scanned, as determined in block 74, and if at least one update has been stored in the packet buffer, as determined in block 76, transmission of the packet is initiated, in block 78. Then the destination pointer is saved as dsave(n), as indicated in block 80, and processing continues by incrementing the neighbor pointer n (blocks 54, 56, 58), and returning to block 52 to find another free link to a neighboring router.
  • the method steps described with reference to FIG. 5 initiate the transmission of distance vector update items, packing as many as will fit into each information packet transmitted a neighboring router.
  • the appropriate Send Flag SF(d,n) is reset to zero and the sequence number of the packet in which the update was transmitted is stored in the sequence number field SN(d,n) of the distance vector, to indicate that an acknowledgment is being awaited.
  • An update acknowledgment message contains the information shown in FIG. 2c, and includes a code indicating the type of message, and a sequence number identical to the sequence number of the information packet of which the receipt is being acknowledged. Inherent in the acknowledgment message is its source, since the identity of the router that originates the acknowledgment will be contained in a message header.
  • any distance vector items are found to have the sequence number x, these are modified by clearing the sequence number to zero, and by making sure that the Send Flag is also zero, as indicated in block 90.
  • the destination pointer is incremented (block 92), and checked for its maximum value in block 94. Until the maximum value is reached, scanning continues in block 88 until all the destinations in the distance vector have been checked. Then return is made to block 82 to wait for another acknowledgment message.
  • the function of the steps illustrated in FIG. 7 is to process received distance vector update messages.
  • the receiving router's distance vector is appropriately updated, as indicated in block 98. That is to say, the receiving router's shortest distances to the destinations with which the received update was concerned are recomputed.
  • an acknowledgment message is generated, as indicated in block 100, including the same sequence number that was contained in the received update message packet.
  • FIG. 8 illustrates the functions performed to handle situations in which no acknowledgment is received after transmitting an information packet that contains distance vector update items. Basically, this aspect of the method triggers retransmission of distance vector update items if no acknowledgment is received within a selected time period, such as T seconds. In this illustrative flowchart, a "cleanup" operation is performed every second, although it will be understood that any periodic time may be used.
  • the last sequence number transmitted is saved (block 104). Then the sequence number transmitted T seconds earlier is retrieved (block 106). Performing these operations requires a cyclically accessed sequence of T storage locations. A scan is then performed of the entire matrix of sequence numbers SN(d,n) stored in the distance vector. Pointers n and d are initialized, in blocks 108, 110; then each sequence number SN(d,n) is compared (in block 112) with the retrieved sequence number from T seconds earlier, designated SN T .
  • SN(d,n) is less than or equal to SN T , then it may be concluded that this item of the distance vector was transmitted to router n more than T seconds ago and that no acknowledgment has been received.
  • the destination pointer d is incremented (block 116) until all destinations have been scanned (block 118).
  • the neighbor pointer n is incremented (block 120) until all the neighbors have been scanned (block 122), which concludes processing until the next one-second period has elapsed, as determined in block 102.
  • sequence numbers are obtained from a large counter, they will recur in a cyclic fashion. Therefore, a definition is required for ordering of the numbers in a circular sequence number space. Given a space of sequence numbers ranging from 0 to 2N-1, a sequence number i is defined to be "greater than" a sequence number j if, and only if, one of the following arithmetic inequalities is true: either N > (i-j) > 0 or (j-i) > N.
  • the present invention represents a significant advance in the field of interconnected networks of computers.
  • the invention provides a simple and efficient technique for transmitting updated distance vector information among routers that are connected by datagram point-to-point links.
  • the manner in which an information packet sequence number is used provides for positive acknowledgment of update messages, but does not require that an update be acknowledged before a subsequent update is delivered. Therefore, rapidly occurring changes can be more quickly delivered to other routers, without waiting for acknowledgment of each previous update message.
  • the invention also provides for retransmission of update messages in the event that acknowledgments are not received within a selected time period.
  • An important advantage of the invention is that these features are implemented with only modest demands on storage facilities. It will also be appreciated that, although an embodiment of the invention has been described in detail for purposes of illustration, various modifications may be made without departing from the scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.

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Claims (14)

  1. Verfahren zum Aktualisieren von Abstandsvektoren in einer Netzwerktopologie, die mehrere Ziele und mehrere Router umfaßt, von denen einige durch Datagramm-Punkt-zu-Punkt-Links verbunden sind, wobei das Verfahren folgende Schritte umfaßt:
    Erfassen (40) von Änderungen in einem in einem Router (10) gespeicherten Abstandsvektor;
    bei der Erfassung einer Abstandsänderung für ein Ziel in dem Abstandsvektor, Setzen eines Send-Flags (48), das diesem Ziel und jedem benachbarten Router entspricht;
    Erfassen (52) der Verfügbarkeit eines Links (16) an einen ausgewählten benachbarten Router n;
    Übertragen (78) eines Informationspakets an den benachbarten Router n über den verfügbaren Link, wobei das Informationspaket so viele Abstandsvektor-Aktualisierungselemente wie möglich enthält, die von dem dem Router n zugeordneten Send-Flags markiert werden;
    vor dem Übertragen des Pakets Auswählen einer eindeutigen Folgezahl zur Übertragung mit dem Paket;
    Speichern der Folgezahl in einem Folgezahlfeld SN(d,n) für jedes mit dem Paket übertragene Aktualisierungselement;
    Empfangen (82) einer Bestätigungsnachricht von dem benachbarten Router n, die die gleiche eindeutige Folgezahl enthält, die mit dem Informationspaket übertragen wurde; und
    Löschen (90) des Folgezahlfelds in jeder Position des Abstandsvektors, in der die eindeutige Folgenummer gespeichert ist, um eine erfolgreiche Übertragung des entsprechenden Abstandsvektor-Aktualisierungselements anzugeben.
  2. Verfahren gemäß Anspruch 1, ferner mit folgenden Schritten:
    Abtasten für die Verfügbarkeit von Links zu weiteren benachbarten Routern; und
    Wiederholen für jeden verfügbaren Link die Schritte des Übertragens eines Informationspakets, Auswählen einer eindeutigen Folgenummer, Speichern der Folgenummer in den Abstandsvektor, Empfangen einer Bestätigungsnachricht und Löschen der geeigneten Folgezahlfelder in dem Abstandsvektor, wodurch Abstandsvektor-Aktualisierungen an alle benachbarten Router übertragen werden.
  3. Verfahren gemäß Anspruch 2, bei dem der Schritt des Übertragens des Informationspakets umfaßt:
    Abtasten des Abstandsvektors nach Aktualisierungselementen, die noch nicht übertragen wurden;
    Speichern jedes ermittelten Aktualisierungselements in dem Informationspaket; und
    wenn das Paket voll ist, Initiieren seiner Übertragung.
  4. Verfahren gemäß Anspruch 3, bei dem der Schritt des Übertragens des Informationspakets den folgenden zusätzlichen Schritt umfaßt:
    Prüfen, um zu bestimmen, ob eine ausgewählte Anzahl von Zielelementen in dem Abstandsvektor abgetastet wurden; und
    falls so, Initiieren des Übertragung des Pakets sogar dann, wenn es nicht voll ist.
  5. Verfahren gemäß Anspruch 3, bei dem der Schritt des Abtastens des Abstandsvektors auf einer zyklischen Warteschlangenbasis (round-robin basis) durchgeführt wird, wobei das Abtasten für einen bestimmten benachbarten Router bei einem Zielelement beginnt, das dem letzten vor dem Initiieren der Übertragung des letzten Informationspakets an den gleichen benachbarten Router abgetasteten Element folgt.
  6. Verfahren gemäß Anspruch 2, ferner mit folgenden Schritten:
    Empfangen an einem benachbarten Router eines Abstandsvektor-Aktualisierungspakets;
    Aktualisieren eines Abstandsvektors an dem empfangenen Router gemäß der in dem Vektor-Aktualisierungspaket empfangenen Information; und
    Übertragen einer Bestätigungsnachricht an den Router von dem das Aktualisierungspaket empfangen wurde, wobei die Bestätigungsnachricht die gleiche eindeutige Folgezahl umfaßt, die in dem empfangenen Aktualisierungspaket enthalten war.
  7. Verfahren gemäß Anspruch 2, ferner mit folgenden Schritten:
    Periodisches Speichern der Folgezahl des letzten von dem Router übertragenen Informationspakets;
    periodisches Wiedergewinnen der Folgezahl des letzten, um eine ausgewählte Zeitspanne vorher übertragenen Informationspakets;
    Abtasten des Abstandsvektors nach den Folgezahlen, die gleich oder kleiner als die wiedergewonnene Folgezahl sind, wobei diese Zahlen die Abstandsvektor-Aktualisierungselemente angeben, die übertragen jedoch für länger als die ausgewählte Zeitspanne nicht bestätigt wurden;
    Löschen aller ermittelten Folgezahlen, die in dem vorhergehenden Schritt ermittelt wurden; und
    Setzen der Send-Flags entsprechend der in dem vorhergehenden Schritt gelöschten Folgezahlen, wodurch die den unbestätigten Übertragungen entsprechenden Aktualisierungselemente zur Neuübertragung markiert werden.
  8. Vorrichtung zum Aktualisieren von Abstandsvektoren in einer Netzwerktopologie, die mehrere Ziele und mehrere Router (10) umfaßt, von denen einige mit Datagramm-Punkt-zu-Punkt-Links verbunden sind, wobei die Vorrichtung umfaßt:
    Mittel (40, 34) zum Erfassen von Änderungen in einem in einem Router gespeicherten Abstandsvektor;
    Mittel (48), das auf die Erfassung einer Abstandsänderung für ein Ziel in dem Abstandsvektor anspricht, zum Setzen eines Send-Flags (SF), das diesem Ziel und jedem benachbarten Router entspricht;
    Mittel (52) zum Erfassen der Verfügbarkeit eines Links (16) an einen ausgewählten benachbarten Router n;
    Mittel (18) zum Übertragen eines Informationspakets an den benachbarten Router n über den verfügbaren Link, wobei das Informationspaket so viele der Abstandsvektor-Aktualisierungselemente wie möglich enthält, die durch dem Router n zugeordnete Send-Flags markiert sind;
    Mittel, die vor dem Übertragen des Pakets betreibbar sind, zum Auswählen einer eindeutigen Folgezahl (62) zur Übertragung mit dem Paket;
    Mittel zum Speichern der Folgezahl in einem Folgezahlfeld SN(d,n) für jedes mit dem Paket übertragene Aktualisierungselement;
    Mittel (31) zum Empfangen einer Bestätigungsnachricht von dem benachbarten Router n, die die gleiche eindeutige Folgezahl enthält, die mit dem Informationspaket übertragen wurde; und
    Mittel (90) zum Löschen des Folgezahlfelds in jeder Position des Abstandsvektors, bei der die eindeutige Folgezahl gespeichert ist, um eine erfolgreiche Übertragung des entsprechenden Abstandsvektor-Aktualisierungselements abzugeben.
  9. Vorrichtung gemäß Anspruch 8, bei der:
    die Vorrichtung ferner Mittel zum Abtasten der Verfügbarkeit von Links an weitere benachbarte Router umfaßt;
    und die Mittel zum Übertragen eines Informationspakets, Auswählen einer eindeutigen Folgezahl, Speichern der Folgezahl in dem Abstandsvektor, Empfangen einer Bestätigungsnachricht und Löschen der passenden Folgezahlfelder in dem Abstandsvektor alle betreibbar sind, um Abstandsvektor-Aktualisierungen an weitere benachbarte Router zu übertragen.
  10. Vorrichtung gemäß Anspruch 9, bei der die Mittel zum Übertragen des Informationspakets umfassen:
    Mittel zum Abtasten des Abstandsvektors nach Aktualisierungselementen, die noch nicht übertragen wurden;
    Mittel zum Speichern jedes ermittelten Aktualisierungselements in dem Informationspaket; und
    Mittel, das aktiviert wird, wenn das Paket voll ist, zum Initiieren seiner Übertragung.
  11. Vorrichtung gemäß Anspruch 10, bei der die Mittel zum Übertragen des Informationspakets umfassen:
    Mittel zum Prüfen, um zu bestimmen, ob eine ausgewählte Anzahl von Zielelementen in dem Abstandsvektor abgetastet wurden; und
    Mittel, das auf das zuletzt angeführten Mittel ansprecht, zum Initiieren einer Übertragung des Pakets sogar dann, wenn es nicht voll ist.
  12. Vorrichtung gemäß Anspruch 10, bei der:
       die Mittel zum Abtasten des Abstandsvektors auf einer zyklischen Warteschlangenbasis (round-robin basis) arbeiten, wobei das Abtasten für einen bestimmten benachbarten Router bei einem Zielelement beginnt, das dem letzten vor dem Initiieren der Übertragung des letzten Informationspakets an den gleichen benachbarten Router abgetasteten Element folgt.
  13. Vorrichtung gemäß Anspruch 9, ferner mit:
    Mittel zum Empfangen an einen benachbarten Router eines Abstandsvektor-Aktualisierungspakets;
    Mittel zum Aktualisieren eines Abstandsvektors an dem empfangenden Router gemäß der in dem Vektor-Aktualisierungspaket empfangenen Informationen; und
    Mittel zum Übertragen einer Bestätigungsnachricht an den Router von dem das Aktualisierungspaket empfangen wurde, wobei die Bestätigungsnachricht die gleiche eindeutige Folgezahl umfaßt, die in dem empfangenen Aktualisierungspaket enthalten war.
  14. Vorrichtung gemäß Anspruch 9, ferner mit folgenden Schritten:
    Mittel zum periodischen Speichern der Folgezahl des letzten, von dem Router übertragenen Informationspakets;
    Mittel zum periodischen Wiedergewinnen der Folgezahl des letzten, um eine ausgewählte Zeitspanne vorher übertragenen Informationspakets;
    Mittel zum Abtasten des Abstandsvektors nach den Folgezahlen, die gleich oder geringer als die wiedergewonnene Folgezahl sind, wobei diese Zahlen Abstandsvektor-Aktualisierungselemente angeben, die übertragen jedoch für länger als die ausgewählte Zeitspanne nicht bestätigt wurden;
    Mittel zum Löschen aller ermittelten Folgezahlen, die in dem vorhergehenden Schritt ermittelt wurden; und
    Mittel zum Setzen der Send-Flags entsprechend der durch den zuletzt angeführten Schritt gelöschten Folgezahlen, wobei die den nicht bestätigten Übertragungen entsprechenden Aktualisierungselemente zur Neuübertragung markiert werden.
EP91308670A 1990-10-15 1991-09-24 Verfahren und Gerät zur Entfernungsvektorlenkung in Punkt-zu-Punkt Datagram Verbindungen Expired - Lifetime EP0481610B1 (de)

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US597144 1990-10-15

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US5243592A (en) 1993-09-07
EP0481610A3 (en) 1994-12-07
DE69132633T2 (de) 2002-04-18
JPH04265037A (ja) 1992-09-21
CA2053397A1 (en) 1992-04-16
EP0481610A2 (de) 1992-04-22
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